Reflecting the advancement of fine processing technology, large scale integration (LSI) has ever been increasing in integration, function, and performance. As a result, the circuit resistance and condenser capacitance between interconnection lines (called parasitic resistance and parasitic capacitance, respectively) increase to increase not only power consumption but retardation time, which is a great cause of reduction of signal speed of a device.
It has therefore been demanded to reduce parasitic resistance or parasitic capacitance. One of the solutions is to cover the peripheries of interconnection lines with an interlayer dielectric film to reduce the parasitic capacitance so as to cope with speeding up of devices. In this case, the interlayer dielectric film must have excellent heat resistance withstanding a thin film formation step for producing a mounting substrate or post steps, such as chip bonding and pin insertion mounting.
Polyimide is widespread as a highly heat-resistant organic material for this use but, containing a highly polar imido group, unsatisfactory from the standpoint of low dielectric properties and low water absorbability.
On the other hand, polyphenylene is known as a heat-resistant organic material containing no polar group. Because polyphenylene is, while excellent in heat resistance, inferior in solubility in organic solvents, it is a practice generally followed to introduce a side chain. Polyphenylene having a side chain includes polymers described in U.S. Pat. No. 5,214,044, WO 96/28491, and EP 629217.
These polymers have a basic structure mainly comprising a poly-p-phenylene structure and, in some cases, a flexible monomer unit. They are soluble only in specific organic solvents and have poor processability. Besides, many of them carry a polar group or an alkyl group as a side chain and therefore fail to fully satisfy the requirements of heat resistance and low dielectric properties.
Further, most of these conventional polymers are produced by starting with aromatic dichloro compounds such as p-dichlorobenzene derivatives. When a fluoroalkyl group or an aryl group is to be introduced as a side chain in an attempt to obtain a heat-resistant low-dielectric material from such an aromatic dichloro compound, there are accompanying disadvantages, such that the synthesis of the monomer becomes complicated, the monomer cannot be secured in a stable manner, and the degree of polymerization does not rise sufficiently on account of the steric hindrance of the side chain.
Thus there has been found no polyphenylene that could fulfill the requirements of heat resistance, low dielectric properties and processability and that could be produced economically.